Combustible hot top



United States Patent 3,495,995 COMBUSTIBLE HOT TOP Michael E. La Bate, deceased, late of Ellwood City, Pa., by Pittsburgh National Bank, executor, P.0. Box 747, Pittsburgh, Pa. 15230 No Drawing. Filed Apr. 18, 1968, Ser. No. 722,493 Int. Cl. B28b 7/36; C04b 35/68; C21c 7/00 U.S. Cl. 106-3822 ABSTRACT OF THE DISCLOSURE A combustible hot top composition incorporating a material rendering the hot top formed of the composition immune to moisture damage.

This invention relates to a combustible hot top composition and more specifically to a combustible hot top composition immune to moisture damage.

A further object of the invention is the provision of a combustible hot top composition from which a consumable hot top may be formed for use on an ingot mold in which ingots of metal are formed and wherein the hot top composition is capable of withstanding moisture which has heretofore caused a softening and partial distintegration of combustible hot tops.

A still further object of the invention is the provision of a combustible hot top composition that results in a combustible hot top that is sufficiently strong so that the rigid portions of the hot top will suitably hold molten metal poured therein when the same is positioned on the ingot mold.

In forming iron and steel ingots, hot metal is poured into ingot molds which contain at the top portion what is generally known in the trade as a hot top. These hot tops usually are prepared from a mixture of refractory and combustible materials and are placed in the uppermost portion of the mold for purposes of insulating and supplying heat to the top of the ingot.

Normally, without the use of such hot tops the upper portion of an ingot cools at a rate much faster than the bottom and thus forms what is known as piping or shrinking in the ingot due to the shrinking of the metal as it cools in contact with the inner walls of the ingot mold. In order to maintain a pool of molten metal that will flow downwardly into the ingot as it cools and shrinks, it is presently the practice to use a hot top which is positioned partially within the upper end of the ingot mold and extends outwardly therabove and is capable of maintaining a pool of molten metal over the piping area while at the same time supplying or preventing heat from escaping from the top of the ingot mold.

Until recently, it was customary in the steel industry to utilize hot tops formed of refractory materials, which provided a somewhat slower rate of cooling or chilling of the metal contained than the rate of cooling or chilling of the metal in the body of the ingot mold. The relative ditference in the cooling or chilling rate was not sufiiciently great to insure the absence of piping or shrinking in the ingot, and improved hot tops have therefore recently been adopted by the steel industry and which hot tops are formed of combustible compositions so that the hot tops are completely consumed or disintegranted which avoids the necessity of removing them from the ingot, and, more importantly, such combustible hot tops have a considerably higher insulating value which respect to the retention of desirable molten metal temperatures in the metal therein which insures the avoidance of piping or shrinking in the ingot thereinunder.

The combustible hot top industry has been faced with the problem of supplying the steel industry with suitable 1 Claim Y combustible hot tops which are both strong enough to maintain their shape while in position on the ingot mold and while they are holding a pool of molten metal, as hereinbefore described, and additionally capable of maintaining their shape and proper rigidity and structure from the time they are manufactured until they are finally used and which may obviously cover a period of weeks and/or months, and during which time the combustible hot tops are subjected to various atmospheric conditions which have heretofore tended to rapidly deteriorate the combustible hot tops.

Combustible hot tops heretofore known in the art have generally comprised suitable shapes, for the particular ingot mold on which they were to be positioned formed of such material as sawdust or wood particles, dolomite which is essentially calcium magnesium carbonate, and a binder material such as sodium silicate in a Water solution or a resin urea-formaldehyde solution. These materials when properly mixed and shaped into the desired hot top components and dried, preferably by subjecting the same to heated air in a suitable oven, have a remarkable ability to contain molten metal for a sufficient period of time to insure the desired results in the metal ingot being poured. The hot tops, however, had the characteristic of absorbing moisture from the atmosphere even though Wrapped in suitable protective coverings, such as polyethylene sheet material and the like, and upon continued exposure to the atmosphere the combustible hot top heretofore known had a tendency to deteriorate as the relative humidity increased and the absorption of water from the atmosphere progressed.

In order that combustible hot tops formed from the combustible hot top composition would avoid water absorption and deterioration, it has been found that improved hot tops can be prepared from essentially the same combustible hot top composition as heretofore known with the addition of magnesium oxide (MgO) in a relatively small quantity.

Accordingly, it is a further object of the invention to provide a composition for preparing a relatively thin combustible hot top having improved body strength and relatively high resistance to water absorption and moisture caused disintegration.

It is still another object of the invention to provide a combustible hot top composition incorporating a material rendering hot tops formed therefrom moisture resistant and capable of a relatively long life between forma tion and ultimate use on the ingot mold.

The present invention provides for an improved combustible hot top composition.

With the foregoing and other objects in view which will appear as the description proceeds, the invention resides in the combination of certain ingredients in a combustible hot top composition and in the details of the composition hereinafter described and claimed, it being the intention to cover all changes and modifications of the example of the invention herein chosen for purposes of the disclosure, which do not constitute departures from the spirit and scope of the invention.

It has been found that improved hot tops can be prepared from the composition consisting essentially of calcium magnesium carbonate, ground wood, sodium silicate solution and magnesium oxide. More specifically, hot tops of improved body strength and moisture-absorption resistance can be prepared from a composition comprising essentially 40 lbs. of sawdust, 140 lbs. of raw dolomite, lbs. of sodium silicate solution and 6 to 8 lbs. of magnesium oxide of 93% to 95% purity.

In preparing hot tops from this improved composition, the specific quantities of sawdust, dolomite, sodium silicate solution and magnesium oxide are mixed in a batch- 3 N type mixer to obtain'uniform distribution of the components. The mixture is then formed into the desired shape and is then dried and cured in an oven at suitable temperatures to form a hard structurally strong shape.

It has also been found that improved hot tops can be prepared irom a slightly modified composition consisting essentially of calcium magnesium carbonate, ground wood, sodium silicate solution and asbestos and magnesium oxide. More specifically, hot tops of improved body strength and moisture-absorption resistance can be prepared from a coinposition comprising essentially 40 lbs. of sawdust, 140 lbs. of raw dolomite, 80 lbs. sodium silicate solution, lbs, asbestos fiber and 4 lbs. of magnesium oxide. The specific quantities of the sawdust, raw dolomite, sodium silicate solution asbestosfiber and magnesium oxide are mixed in a batch-type mixer to obtain uniform distribution of the components. The mixture is then formed into the desired shape and is then dried and cured in an oven at suitable temperatures.

The sodium silicate binder usually is an aqueous solution containing about 50% by weight of sodium silicate. The silicates used in preparingthese 50% aqueous solu tions may vary from Na Oa2/3SiO to Na O.3.9SiO and differ in alkalinity from a pH of 13.2 to 10.8, respec-' tively. A typical solution comprises about 53% by weight water, 31% by weight SiO and 13.9% by weight N320.

It will occur to those skilled in the art that during the heating cycle the reaction of the silicates with the carbonate goes to completion giving increased body strength to the finished product. At this time, the reaction is substantially improved by the presence of the magnesium oxide and the resulting product has a desired characteristic hereinbefore'set forth. It will further be observed that approximately 15% of the total mixture is water which is added as part of the aqueous solution of sodium silicate. Most of this water is removed at temperatures at which the product is cured. It will occur to those skilled in the art that initially the temperatures in the curing process may be as high as 370 F. because of the presence of water vapors and that the water vapor prevents the sawdust from charring at these temperatures. As the water is removed in the drying process, the temperature is normally reduced to avoid charting ;;of the sawdust particles. I I

It.will be apparent that in the first of the above-given examples the sawdust equals approximately 15% of the cornosition; the raw dolomite equals approximately 52% of the composition; the sodium silicate solutions equals approximately 29 /2% of the composition, and the magnesium oxide equals approximately 3 /z% of the composition. 7 5 I It will further be seen that the second of the aforesaid examples comprises a composition in which the 40 lbsf'of sawdust equals approximately 15%of the composition; the 140 lbs. of dolomite equals aproximately 52% of the composition; the 80 lbs, ofsodium silicate solution equals approximately 29 /2% of the composition; the 5 lbs. of asbestos equal approximately 1%% of the composition;

and the 4 lbs. of magnesium oxide equals approximately 1% of the composition.

It will occur to those skilled in the art that variations in the quantities of the several ingredients heretofore noted in the examples of the invention may be made. For example, the amount of sawdust may be varied from 35 lbs. to 45' lbs. theamount of raw dolomite may be varied from 130 lbs. to '145 lbs: The sodium silicate solution may be varied from lbs. to 85 lbs. and the magnesium oxide may be varied from 4 lbs. to 10 lbs, In the example wherein the asbestos is used, the same proportionate variation may be made. ii

It will also occur to those skilled in the art that the basic mixture may be altered by substituting an equal quantity by weight of small sized wood chips, rice hulls, wheat kernels or their equivalent for the. sawdust? A still further variation forming a suitable mixture comprises substituting sintered granulated blast furnace slag or finely ground fired clay (grog) for the dolomite in equilavent quantities. It has also been determined that urea-formaldehyde resin in the amount of 5.0 lbs. by weight can be used as a binder rather :than the lbs. of sodium silicate solution hereinbefore specified. The magnesium oxide has been found to react in the same manner with these substitutions of equivalent materials as with the examples hereinbefore given.

It will be seen that the ignproved hot top composition results in, hot top structures having a superior green strength which is important in the initial handling of the shapes formed therefrom. This advantage is in addition to the ability of the composition to resist moisture absorption and ultimate deterioration therefrom.

It will thus be seen that an improved hot top composition meeting the several objects of the invention has References Cited UNITED STATES PATENTS 3,109,211 11/1963 Wagner et a1; l0638.35 3,212,742 10/1965 La Bate 10638.3 X 3,297,296 1/1967 Edstrom et al. 249--l97 3,300,322 1/1957 De 'Geer 106-3835 TULIUS FROME, Primary Examiner L. HAYES, Assistant Examiner US. 01. X.R 1063 5.3; 249197, 201 

